This invention concerns an improved method and apparatus for shaping thermoplastic tubes. As used herein, the term "tube" includes hoses, pipes and similar conduits, whether of single or multi-layer construction.
U.S. Pat. No. 5,200,124 owned by the assignee of this invention discloses a method and apparatus for shaping a thermoplastic tube by contactless heating a pre-formed bend region of the tube with a pulsed emission of infra-red radiation to conform the tube to a required bend configuration followed by cooling to retain the required bend configuration while the tube is supported on a former.
The pulsed emission is effected by switching one or more remote infra-red sources on and off to provide a series of separate pulses of which the duration of each pulse and the interval between successive pulses is timed.
For a given pulse duration and pulse interval, the overall number of pulses to achieve the required heating can be calculated. For example, a heating cycle may consist of 20 pulses of which the duration of each pulse is 1.2 seconds and the interval between successive pulses is 2.0 seconds.
Although the method and apparatus disclosed in U.S. Pat. No. 5,200,124 generally performs satisfactorily, it has been found that such time based control of the heating cycle can cause problems if substantial differences in ambient temperature occur requiring "running changes" to be made to the number of pulses.